There is an ever increasing need in industry for data privacy and/or security. In the communications field data being transmitted via radio communication or telephone lines are susceptible of interception and unauthorized user alteration. Various cryptographic systems have been proposed to reduce or eliminate this vulnerability of data to an unauthorized user or penetrator.
In the field of computers the unauthorized access of data may be obtained by accessing various storage devices or intercepting messages being transmitted between terminals or between terminals and the host of a remote access computer network.
Current privacy laws place an increasingly greater burden upon the computer manufacturer and user to guard the privacy of the data of individuals or businesses for unauthorized penetration and use. Such unauthorized access to the computer can have many ramifications too numerous to mention going from the mere access of confidential business or personal data by someone who has no real need to know this information, to the unauthorized access of bank or payroll records which in an exagerated case could cause money to be improperly dispensed, or incorrectly credited to the wrong person's account, resulting in greater potential financial losses.
Many schemes have been proposed in the past for preventing various types of penetration.
For example, in a conventional multi-program, time shared computer system as is commonly in use today, given users are assigned areas of memory to which they are allowed access and they are further given special identifier keys which associate a range of memory addresses accessable to the particular user. In normal operation, if a user attempts to incorrectly access a portion of memory not assigned, the system will cause a security interrupt. However, this latter form of operation assumes that a problem program would be operating in the problem or non-privileged state. When in the supervisory or privileged state the system, in normal usage, would be allowed access to any portion of the computer for any purpose, including modifications of the operating system itself. It is apparent that if an unauthorized user or pentrator is able to subvert the normal security measures and cause the "privileged state" code in the program status word (PSW) of the system to be illegally set to "privileged", with most current systems, such a penetrator would have wide access to many portions of the system.
In the past such situations have occurred through errors in the control program or possibly unusual knowledge and capabilities on the part of a programmer who has been able to devise means of altering the `state` control bit of the program status word which specifies the state of this system in computers, such as the IBM System 360 and 370 series.
Once the penetrator has gained access to the "privileged" operation set, he is able to interrogate and/or alter the physical control parameters or states of the system which are supposed to be available to and under control of only the system supervisor.
Thus, a basic need in the current CPU architecture is for improved means of assuring operating system security from unauthorized penetrators. Such security should at least be available at any time after the initial program load (IPL) which, of course, assumes the integrity of the programmers and all personnel doing such IPL.